Recently, researches and development works for biped walking robots that perform walking movement in which a human walking pattern is imitated are conducted in various companies and development organizations. When a biped walking robot performs walking movement in which a human walking pattern is imitated, the control of balance at the time of walking is necessary in order to achieve stable walking movement.
The control of balance at the time of walking in a biped walking robot is performed by controlling the upper half body and the lower half body of the robot such that the robot should stably walk on the center of floor reaction forces which are the reaction forces received by the robot from the floor at the time of walking. Specifically, during the time after the walking robot raises one leg until lands it, the upper half body and the lower half body are controlled such that the center of floor reaction forces should be located within the foot on the ground contacting side, so that the control of balance at the time of walking is performed. Further, in order that the robot should walk smoothly without falling, the acceleration of the robot at the time of walking need be synchronized with the movement of the limbs. Thus, at each time that a foot of the robot lands, the movement of the foot on the landed side is synchronized with the acceleration of the robot such as to be continued smoothly to the subsequent walking movement.
Nevertheless, in the control for walking in a biped walking robot in the prior art, the robot has been controlled such that the center of floor reaction forces should be located at a desired position. This has caused a problem that complicated calculations are necessary. In particular, the complicated calculations in the control for walking have become necessary at each time that various factors such as the shape, the size, the mass distribution, the speed, and the acceleration that depend on the robot and various factors such as a coefficient of friction, a level difference, and an inclination that depend on the floor on which the robot walks have varied. This has caused a problem of huge calculation cost.
Further, in the prior art method in which the hip position is controlled by inverse kinematics such that the center of floor reaction forces should be located at a desired position, in order that singularity should be avoided in the inverse kinematics arithmetic operation, the walking has been performed in a state that the knee joints of the limbs are bent. This has caused a problem of unnaturalness in the appearance of the walking state. Further, in the state that the knee joints are bent, an excessive load occurs in the motor for driving each joint. This has caused a problem in the durability and a problem of increase in the power cost.
Furthermore, when synchronizing is performed at the time of landing of a foot of the robot, the timing of synchronization becomes intermittent. Thus, the calculation results concerning the synchronization become discrete. This has caused a problem that smooth walking in the entire walking movement becomes difficult.